Light emitting diode (LED) lighting systems are becoming more prevalent as replacements for existing lighting systems. LEDs are an example of solid-state lighting (SSL) and have advantages over traditional lighting solutions such as incandescent and fluorescent lighting because they use less energy, are more durable, operate longer, can be combined in multiple color arrays that can be controlled to deliver virtually any color light, and generally contain no lead or mercury. In many applications, one or more LED dies (or chips) are mounted within an LED package or on an LED module, which may make up part of a lighting unit, lighting system, lamp, “light bulb” or more simply a “bulb,” which includes at least one power supply (also called a “driver” or “driver circuit”) to power the LEDs.
Drivers or power supplies may be used in electronic applications to convert an input voltage to a desired output voltage to power electronic devices such as the LEDs of a lamp or lighting system. Some power supplies may be classified as either a linear power supply or a switched-mode power supply. Switched-mode power supplies may be configured to operate more efficiently than linear power supplies. A switched-mode power supply may include a switching device that, when switching on and off, stores energy in an inductor or similar energy storage element and discharges the stored energy to an output of the switched-mode power supply. The switching device may be controlled by a control circuit or controller, which outputs switching signals to turn the switching device on and off. FIG. 1 illustrates a single-ended primary inductor converter (SEPIC) circuit 100 that can be used in some switched-mode power supplies. The circuit uses two inductors L1 and L2, an inline capacitor Ci, a diode D, and output capacitor Cout, and a transistor Q to provide a switching function. Other commonly used converter circuits include a boost converter and a buck converter. FIG. 2 illustrates a boost converter 200, which has only one inductor L1. FIG. 3 illustrates a buck converter 300, in which switching device Q is in-line with the inductor L1.
While the color of the light emitted from an LED primarily depends on the composition of the material used, its brightness is directly related to the current flowing through the pn junction. Therefore, a driver providing a constant current is desired. A driver for an LED lighting system therefore necessarily includes or acts as a current regulator. FIG. 4 shows a lighting apparatus 400 in which a plural number of LED strings 1 to n are driven by constant current regulators 1 through N. Each current regulator receives an input voltage V and regulates the same or different current through each respective LED string, which includes at least one LED. LED strings 1 to n may generate light of the same color or of different colors depending on the color temperature requirements of the lighting apparatus 400.